Hard-to-weld (HTW) alloys, such as nickel-based superalloys and certain aluminum-titanium alloys, due to their gamma prime and various geometric constraints, are susceptible to gamma prime strain aging, liquation and hot cracking. These materials are also difficult to join when the gamma prime phase is present in volume fractions greater than about 30%, which may occur when aluminum or titanium content exceeds about 3%.
These HTW materials may be incorporated into components of gas turbine engines such as airfoils, blades (buckets), nozzles (vanes), shrouds, combustors, rotating turbine components, wheels, seals, 3d-manufactured components with HTW alloys and other hot gas path components. During operation, components formed from HTW may be subjected to operating conditions which cause portions of the component to be worn down or damaged. By way of example, the tips of turbine airfoils such as blades (buckets) may be worn down over time, reducing efficiency of the turbine. Repairs of such wear are impaired by the difficulty in joining HTW materials, making standard repair techniques difficult. Rebuilding such components using hot processes such as laser cladding or conventional thermal spray yields deposited material which is weakened or cracked by the elevated temperatures. Brazing techniques are unsuitable because braze materials or elements are incorporated into the component which may not meet operational requirements.
Gas turbine components incorporating HTW materials tend to be more expensive than components formed from other materials, and certain HTW materials are more difficult to weld and more expensive than others. Incorporation of these HTW materials may be desirable due to often superior operational properties, particularly for certain portions of components subjected to the most extreme conditions and stresses, but difficulties in repairing gas turbine components with HTW materials may lead to components being discarded due to damage or defects which would otherwise be repairable in components formed from other materials, which is both wasteful and costly. However, the same properties which make HTW materials difficult to repair also make HTW materials difficult to join with other, less expensive and more easily reparable materials.